I'm a big fan of aerial and satellite photography, and was thrilled to discover the original TerraServer several years ago. Though its datasets are black and white and a bit dated, it's still amazing to see familiar areas as photographed from above.

There's now another site called TerraServer, with more recent datasets, including some in higher resolution and color. I'm not sure if it's a successor to the old one or a competitor, but this one offers access to very high resolution data (1 foot in some areas) for a fee. Still the same basic interface, though: web form that lets you search for an address and then click to pan or zoom.

It occured to me that the web is hardly the optimal platform for applications like this. (I happen to believe that it's not the optimal plaform for any application, but that's another discussion.) Specifically, I suspected that a local application could let you zoom and pan smoothly over datasets like this, by fetching image tiles on demand from a server. It's such an obvious idea, I figured somebody must have done it.

Turns out I was right.

I asked a friend of mine if he knew of such an application, and it he grinned. "I worked on one once." TerraVision is a cool open source app that does exactly what I expected: it lets you browse multiresolution image/elevation datasets on the earth interactively. You can load more than one dataset, to provide coarse data over a large region, and more detailed data in specific areas. It all works in a small memory overhead by managing a multiresolution cache of tiles.TerraVision can fetch tiles on demand from a server or operate from datasets on the local disk. Unfortunately, there don't seem to be any active TerraVision servers out there, so you're left to download the handful of datasets they provide (or convert your own from USGS data.) In the bay area, for example, I was only able to browse 25 meter terrain data, which isn't enough to resolve individual houses. Still, very cool, especially for an open source app.Kiril also pointed me to a more polished commercial app that does the same thing. Last night I tried a free 7 day trial of Keyhole LT, and was blown away. Because it's a commercial app, they provide a server with really high resolution data over most major cities, and coarser (but decent) data elsewhere. If you live anywhere near a major city, you can probably zoom in to see your house.Keyhole also lets you do address queries (like MapQuest), which makes it easy to find familiar places. I spent several hours last night exploring all the places I've been, continually amazed at the detail in their dataset.For example, the house we just bought is easily discernable in Keyhole. In fact, behind the house there's a bright blue rectangle, which I realized is the blue tarp on top of the awning in the back yard. As seen from space!If you have a Windows machine with any half-decent graphics hardware I highly recommend you check out Keyhole LT. (It works on my laptop with Intel i815e, so it'll probably work on your computer too.) Find your house. You'll thank me for it.

Thursday, October 16, 2003

Things are finally falling into place. We made an offer on a house two weeks ago, and only now are we done with inspections. Things were touch-and-go for a while because inspection did turn up a zombie infestation.

Well, not zombies, but still something creepy. In the crawlspace under the house, our inspector noted an unusually thick layer of efflorescence (salt deposit). That's a sign of moisture leaching out of concrete (or in our case soil), evaporating, and leaving mineral deposits behind. A little efflorescence is common in basements the world over, but this is a thick layer. Two inches deep in some places. We were concerned that it represented a serious drainage problem under the house, or an adverse condition of the soil.

Some other issues came up as well, and we ended up extending the inspection period so we could bring out some specialists. Things were stressful for a while, but as of last night all of the issues have been resolved. The house, its foundation, and the supporting soil appear to be in great shape, so we're going through with it. We'll close escrow on October 30th, and move in soon thereafter. We're psyched.

The pictures at the right are of the front, back, and two shots of the backyard. These were taken during the general inspection (hence the ladders), and so the cars and paraphernelia are not ours. The house is 4 bedrooms, 3 baths, 2-car garage, 1867 sq. ft.

(For the curious: the soil expert says the house was built in the wettest year ever, and the moisture probably worked its way out over the next season or two. Though he's "never seen anything like it", he claims it's of academic interest and little else. Whew.)

Tuesday, October 7, 2003

Ack! While I wasn't paying attention California flipped out and elected Arnold as Governor! At least, that's CNN's projection, already reported as fact. (I actually was paying attention: I voted today, even though we're in the midst of house inspection hell.)

My only hope is that Arnie is as socially liberal as he claims. The pundits claim he'd never survive the scrutiny of the right wing in the primary of a normal election. That gives me some hope.

As for fiscal policy, it's mostly voodoo to me. Lowering taxes and spending pretend money doesn't sit well with me, but since I'm one of the ones that benefits (in the short term, at least) from lower taxes, I'd love to be proven wrong. Plus, I have no choice--Bush is already doing it to us.